Hindawi Publishing CorporationOrganic Chemistry InternationalVolume 2011, Article ID 325291, 5 pagesdoi:10.1155/2011/325291

Research Article

RuCl3 ·nH2O as Catalyst for Diastereoselective Direct AldolReaction: An Efficient Route to Hormone Steroid Derivatives

Khalil Tabatabaeian, Elahe Keshavarz, Manouchehr Mamaghani, and Nosrat O. Mahmoodi

Department of Chemistry, Faculty of Science, The University of Guilan, P.O. Box 41335-1914, Rasht, Iran

Correspondence should be addressed to Khalil Tabatabaeian, taba@guilan.ac.ir

Received 10 September 2010; Accepted 30 November 2010

Academic Editor: Chao Jun Li

Copyright © 2011 Khalil Tabatabaeian et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

RuIII-catalyzed regio- and diastereoselective direct aldol reaction of progesterone with aromatic aldehydes has been developed ingood yields (58–78%). Advantages of this method include catalytic efficiency, short reaction times, and ease of operation andworkup.

1. Introduction

The aldol reaction is one of the most powerful and usefultools for the construction of carbon-carbon bonds, creatingthe β-hydroxy carbonyl derivatives [1–7]. It provides anatom-economic approach to β-hydroxy carbonyls [8–16],which make up a large family of intermediates for the synthe-sis of biologically active substances and natural products. It isextensively applied in the synthesis of carbohydrates, aminosugars, steroids, and other valuable organic compounds.However, the most classical and conventional aldol reactionwhich involves the mixed aldol reaction between a ketonecontaining α-hydrogen with an aldehyde in the presence ofbase or acid has not been well exploited due to the followingreasons: (1) side reactions such as self-condensation ofthe ketone or/and dimerization of the aldehyde can be aproblem; (2) the harsh reaction conditions employed whichusually require a strong acid or base make it unattractive forthe complex molecule synthesis which contains acid or basesensitive functional groups; (3) the desired aldol product isusually accompanied by dehydrated products, dimmers, andpolymers; (4) low regioselectivity is observed in most of thecases. Therefore, mild reaction conditions are much soughtafter to overcome some, if not all, the above problems.

RuIII salts are well known to catalyze a variety of organictransformations, including Michael reactions [17], oxidationreactions of alkanes [18], oxidative cyanation of amines

[19], and many others [20–22]. We have recently reportedthe organic reactions using catalytic amounts of RuIII [23–27], and the investigation of the chemistry of rutheniumcontinues to be one of the most active areas of organometallicchemistry.

On the other hand, progesterone [28] is one of themost important hormones of the steroidal pregnane series,secreted by corpus luteum and placenta, which can beregarded as a hormonal balancer, particularly of estrogens.It also helps to create a balance of all other steroids andhas intrinsic calming and diuretic properties. Thus, due tothe importance of progesterone to the human body andin continuation of our previous works [29–32] on aldolreactions, we would like to report the formation of β-hydroxyketone derivatives derived from progesterone.

2. Results and Discussion

In our investigation, we found that RuCl3· nH2O caneffectively promote the direct aldol reaction of hormonesteroid, that is, progesterone with different aromatic aldehy-des. Treatment of progesterone (0.24 mmol) with aldehydes(0.24 mmol) in the presence of RuCl3· nH2O (5.8 mol%)and KOH in dioxane at room temperature gave the cor-responding aldol adducts in good yields with completediastereoselectivities.

2 Organic Chemistry International

Table 1: Ruthenium-catalyzed direct aldol reaction of aldehydes with progesterone at room temperature.

Entrya Aldehyde Yield (%)b Time (h) Dr (syn/anti)c

1 2a 4-ClC6H4 71 4.5 >99/<1

2 2b 3-ClC6H4 73 5 >99/<1

3 2c 4-BrC6H4 69 5 >99/<1

4 2d 4-MeSC6H4 78 5.5 >99/<1

5 2e 4-FC6H4 65 6 >99/<1

6 2f 4-NO2C6H4 58 6 >99/<1

7 2g 4-MeC6H4 69 6 >99/<1

8 2h 3-NO2C6H4 58 6 >99/<1aAll products were characterized by 1H NMR, 13C NMR, and IR.bYields after purification by chromatography.cDetermined by 1H NMR analysis.

O

O

H H

HH HH

O

OR H

O

+

R

HO

1 2a–h 3a–h

RuCl3 · nH2ORT, dioxane

Scheme 1

Having established suitable reaction conditions, a seriesof aldehydes were employed to investigate the reaction scope.The results are shown in Table 1. The table demonstratesthat this catalytic reaction can be extended to a wide rangeof aromatic aldehydes with good yields (Scheme 1).

As shown in Table 1, compounds 3a–h have been success-fully synthesized and characterized by typical spectroscopictechniques, namely IR, 1H, and 13C magnetic resonance(NMR). The infrared spectra of these compounds showedthree significant stretching vibrations of (O–H), (C=O),and (C=C) at 3400–3500, 1640–1720, and 1600–1650 cm−1,respectively. Also, in a 1H NMR study, we observed theexistence of the olefinic moiety along with the presence ofthree singlets corresponding to the three methyl protonsof the progesterone skeleton showed the aldehydes reactwith progesterone from side a. Additionally, from the NMRspectrum, it was evident that only one diastereomer hasbeen formed. It is a well-understood phenomenon thatthe lower values of the 1H NMR coupling constants ofthe carbinol protons than 1 Hz clearly indicate the relativestereochemistry of the aldol adducts in favor of the syngeometry [33].

The most plausible mechanism for the aldol reaction ofprogesterone with aldehydes, which rationalizes the forma-tion of products, is presented in Scheme 2. The mechanisminvolves ruthenium enolates which can be trapped by analdehyde to give the aldol products (Scheme 3).

In summary, this paper describes a successful cross-coupling reaction between progesterone and various aro-matic aldehydes in the presence of ruthenium catalyst.The results presented herein show the catalytic role ofRuCl3· nH2O at room temperature in the regio- and

O

O

H

H

Side a

HO

H

R

HORCHO

Scheme 2

diastereoselective aldol reaction between progesterone andaldehydes. From an operational viewpoint, the reactionsdo not require an inert atmosphere and can be performedover a short period of time without preactivation of thedonor substrates (direct aldol reaction). The scope (suchas asymmetric synthesis) and synthetic applications of thisreaction are currently under investigation in our laboratory.

3. Experimental

All reactions were followed by TLC with detection byUV light. IR spectra were recorded on Shimadzu FTIR-8400S spectrometer. 1H NMR spectra were obtained ona Bruker DRX-500 Avance spectrometer and 13C NMRwere obtained on a Bruker DRX-125 Avance spectrometer.Samples were analyzed in CDCl3, and the chemical shiftvalues are reported in ppm relative to TMS as the internalreference. Elemental analyses were made by a Carlo-ErbaEA1110 CHNO-S analyzer and agreed with the calculatedvalues. The isolation of pure products was carried out viapreparative thin layer chromatography (silica gel 60 GF254,Merck). Excess of solvent was evaporated under reduced

Organic Chemistry International 3

DioxaneDioxene

[Ru] [Ru]H2

O

O

H

H

H

H

H O

O

H

R

R

ORuO

H

R

HO−O

KOH RT

RuCl3 · nH2O

Scheme 3

pressure at a bath temperature of 50 and 60◦C. All solvents,organic and inorganic compounds, were purchased fromMerck and Fluka and used without further purification.

3.1. Typical Procedure for Synthesis of Aldol Products. Acatalytic amount of RuCl3· nH2O (3 mg, 0.014 mmol) wasadded to a vial containing aldehyde (0.24 mmol), proges-terone (75.5 mg, 0.24 mmol), KOH (14 mg, 0.25 mmol),dioxane (1 mL) and stirred at room temperature (monitoredby TLC). After the indicated reaction time, the reactionmixture was purified by thin layer chromatography (silicagel, EtOAc-petroleum ether, 6 : 12) providing the aldoladduct.

3.1.1. Product (3a). [α]36D + 170 (c 1.0, CHCl3), yellow oil;

IR (neat) (υmax/cm−1): 3450, 3100, 2980, 1700, 1680, 1650,1460. 1H NMR (500 MHz, CDCl3): δH (ppm) 0.71 (s, 3H),1.30 (s, 3H), 2.20 (s, 3H), 0.70–2.82 (m, 19H), 3.14 (s, OH),5.78 (s, 1H), 6.24 (d, J = 0.8 Hz, 1H), 7.31 (m, 4H). 13CNMR (125 MHz, CDCl3): δC (ppm) 14.4, 14.5, 25.1, 25.3,27.5, 28.2, 28.2, 43.0, 47.7, 48.1, 55.2, 57.5, 58.2, 68.6, 129.7,130.2, 130.7, 132.9, 134.7, 135.6, 143.6, 191.3, 215.1. (Found:C, 73.94; H, 7.72. Calc. for C28H35O3Cl: C, 73.92; H, 7.70%).

3.1.2. Product (3b). [α]36D + 165 (c 1.0, CHCl3), yellow oil;

IR (neat) (υmax/cm−1): 3450, 2910, 1700, 1680, 1645, 1590,1575. 1H NMR (500 MHz, CDCl3): δH (ppm) 0.70 (s, 3H),1.20 (s, 3H), 2.20 (s, 3H), 0.87–2.75 (m, 19H), 5.96 (s, 1H),6.21 (d, J = 0.5 Hz, 1H), 7.37–7.46 (m, 2H), 7.54–7.56 (m,1H), 7.71–7.73 (m, 1H). 13C NMR (125 MHz, CDCl3): δC

(ppm) 12.4, 16.2, 25.1, 25.2, 27.4, 28.2, 31.3, 47.6, 47.7, 48.0,48.1, 67.5, 70.8, 70.9, 73.3, 73.5, 128.9, 129.2, 129.3, 129.7,129.9, 134.0, 134.2, 135.7, 192.2, 205.1. (Found: C, 73.93; H,7.73. Calc. for C28H35O3Cl: C, 73.92; H, 7.70%).

3.1.3. Product (3c). [α]36D + 168 (c 1.0, CHCl3), yellow oil;

IR (neat) (υmax/cm−1): 3420, 2905, 1680, 1662, 1642, 1540,1420. 1H NMR (500 MHz, CDCl3): δH (ppm) 0.73 (s, 3H),1.22 (s, 3H), 2.18 (s, 3H), 0.87–2.72 (m, 19H), 5.84 (s, 1H),6.24 (d, J = 0.7 Hz, 1H), 7.27–7.35 (m, 4H). 13C NMR(125 MHz, CDCl3): δC (ppm) 14.1, 14.5, 25.0, 26.3, 27.5,28.2, 28.3, 43.1, 47.7, 48.1, 55.2, 57.5, 59.2, 68.6, 129.5, 130.1,

130.7, 132.8, 134.7, 135.5, 143.6, 191.2, 215.0. (Found: C,67.35; H, 7.05. Calc. for C28H35O3Br: C, 67.33; H, 7.01%).

3.1.4. Product (3d). [α]36D + 155 (c 1.0, CHCl3), yellow oil;

IR (neat) (υmax/cm−1): 3450, 3100, 2940, 1680, 1645, 1600,1510. 1H NMR (500 MHz, CDCl3): δH (ppm) 0.71 (s, 3H),1.23 (s, 3H), 2.17 (s, 3H), 2.19 (s, 3H), 0.72–2.82 (m, 19H),3.14 (s, OH), 5.78 (s, 1H), 6.24 (d, J = 0.8 Hz, 1H), 7.25–7.31(m, 4H). 13C NMR (125 MHz, CDCl3): δC (ppm) 13.8, 14.4,15.1, 25.2, 25.3, 27.5, 28.2, 28.2, 43.5, 47.7, 48.5, 55.2, 57.5,58.1, 68.6, 129.7, 130.2, 130.4, 132.7, 134.7, 135.6, 143.6,191.0, 215.1. (Found: C, 74.69; H, 8.12. Calc. for C29H38O3S:C, 74.67; H, 8.15%).

3.1.5. Product (3e). [α]36D + 170 (c 1.0, CHCl3), yellow oil; IR

(neat) (υmax/cm−1): 3450, 3100, 1720, 1640, 1390. 1H NMR(500 MHz, CDCl3): δH (ppm) 0.73 (s, 3H), 1.21 (s, 3H), 2.18(s, 3H), 0.70–2.76 (m, 19H), 5.75 (s, 1H), 6.24 (s, 1H), 7.39–7.42 (m, 4H). 13C NMR (125 MHz, CDCl3): δC (ppm) 12.5,16.0, 25.1, 25.2, 27.5, 28.2, 31.2, 47.6, 47.8, 48.1, 48.4, 67.5,70.7, 70.9, 73.3, 73.5, 128.9, 129.1, 129.3, 129.7, 129.9, 134.0,134.2, 135.7, 192.1, 205.0. (Found: C, 76.73; H, 7.98. Calc. forC28H35O3F: C, 76.71; H, 7.99%).

3.1.6. Product (3f). [α]36D + 175 (c 1.0, CHCl3), yellow oil;

IR (neat) (υmax/cm−1): 3455, 3070, 2985, 1700, 1680, 1650,1460. 1H NMR (500 MHz, CDCl3): δH (ppm) 0.71 (s, 3H),1.30 (s, 3H), 2.20 (s, 3H), 0.69–2.80 (m, 19H), 3.15 (s, OH),5.75 (s, 1H), 6.24 (d, J = 0.8 Hz, 1H), 7.34 (m, 4H). 13CNMR (125 MHz, CDCl3): δC (ppm) 14.2, 14.5, 25.0, 25.3,27.4, 28.1, 28.2, 43.0, 47.5, 48.0, 55.2, 57.5, 58.1, 68.5, 129.8,130.2, 130.7, 132.9, 134.7, 135.6, 143.6, 191.2, 215.1. (Found:C, 75.9; H, 7.85. Calc. for C28H35O5N: C, 75.5; H, 7.86%).

3.1.7. Product (3g). [α]36D + 160 (c 1.0, CHCl3), yellow oil;

IR (neat) (υmax/cm−1): 3450, 3090, 2950, 1680, 1645, 1600,1525. 1H NMR (500 MHz, CDCl3): δH (ppm) 0.71 (s, 3 H),1.23 (s, 3 H), 1.45 (s, 3H), 2.19 (s, 3H), 0.70–2.82 (m, 19H),3.12 (s, OH), 5.77 (s, 1H), 6.22 (d, J = 0.8 Hz, 1H), 7.22–7.30(m, 4H). 13C NMR (125 MHz, CDCl3): δC (ppm) 13.9, 14.04,15.1, 25.2, 25.4, 27.5, 28.2, 29.2, 43.5, 48.7, 48.9, 55.2, 58.5,59.1, 71.6, 129.5, 130.1, 130.4, 132.5, 134.5, 135.6, 143.6,

4 Organic Chemistry International

191.1, 215.5. (Found: C, 80.21; H, 8.77. Calc. for C29H38O3:C, 80.18; H, 8.75%).

3.1.8. Product (3h). [α]36D + 162 (c 1.0, CHCl3), yellow oil;

IR (neat) (υmax/cm−1): 3450, 2910, 1700, 1685, 1645, 1590,1555. 1H NMR (500 MHz, CDCl3): δH (ppm) 0.71 (s, 3H),1.22 (s, 3H), 2.21 (s, 3H), 0.85–2.75 (m, 19H), 3.17 (s, OH),5.79 (s, 1H), 6.22 (d, J = 0.8 Hz, 1H), 7.35–7.46 (m, 2H),7.53–7.56 (m, 1H), 7.70–7.72 (m, 1H). 13C NMR (125 MHz,CDCl3): δC (ppm) 12.4, 16.2, 25.0, 25.2, 27.4, 30.2, 31.3,45.6, 47.7, 48.2, 48.5, 67.5, 70.7, 70.9, 73.3, 73.6, 128.9, 129.2,129.3, 129.7, 129.8, 134.1, 134.2, 135.8, 192.2, 205.2. (Found:C, 75.6; H, 7.87. Calc. for C28H35O5N: C, 75.5; H, 7.86%).

Acknowledgment

The authors are grateful to the Research Council of GuilanUniversity for the support of this study.

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